SPRAYING APPARATUS

Abstract: A sprayer head and pan-type coater are used for spraying liquid onto particulate solids. The sprayer head comprises a rotatable disc (4) to deflect droplets created by a centrifuge. An annular cone-shaped curtain of spray is sprayed onto a bed of particulate solids on a horizontal base of a revolving pan (10) of the pan-type coater. Paddles (18) fixed to a frame (11) serve to gently turn the particles in the bed and to move them towards a central outlet.

Description: SPRAYING APPARATUS The present invention relates to a sprayer head for use in spraying liquids onto particulate solids, a pan-type coater for continuous spraying of liquid onto particulate solids, and use of the same. Various types of sprayer head are known for use in spraying liquid onto particulate solids such as pellets, briquets, crumbles, granules, granulates, powders, ground material or the like ("solids" hereinafter) . An atomising head having a hydraulic nozzle with fine holes through which pressurized liquid is sprayed is known, but is susceptible to blockage by particles in the liquid. It is also known to create a liquid spray in an air atomiser by a combination of liquid and air pressure, as used in e.g. car painting equipment. This has larger holes and is less susceptible to blockage. However a wide range of droplet sizes is created. It is also known to create a spray by feeding the liquid to be sprayed onto the surface of a rapidly rotating disc. On contact with the disc, the centrifugal force creates a horizontal curtain of liquid, which can be broken into a fine spray by providing fine protrusions on the perimeter of the disc. Such devices are suitable for creating a horizontal spray to coat solids passed vertically through the spray. However, they are unsuitable for creating a cone-shaped spray for coating solids passing horizontally below the sprayer head. For such applications, a known sprayer head is shown in EP-A-0 349 510. In this system, shown schematically in Figure 1, a centrifuge driven at at speed of between 500 and 6000 rpm is used to break up the liquid into fine droplets. A narrow range of droplet size can be achieved, e.g. 40-60 urn according to rotation speed and liquid properties. The centrifuge comprises a rotatable blade in the form of a cross-beam 1 and a tapered centrifuge housing 2. Liquid is introduced into the centrifuge through an injector 3. The droplets are projected with some force, and the compressed air carries the particles in a downward spray cone. However, there are a number of problems with this type of sprayer. Firstly, large droplets, many times larger than the desired droplet size, can occasionally drip from the cross bar straight downwards under gravity. Secondly, it is difficult to create an annular cone-shaped curtain of spray with such a system. If a stationary deflector is placed under the centrifuge, more large droplets would be created. Such larger droplets are undesirable where the evenness of the distribution of the spray is critical. One such application is in spraying enzymes in very small quantities onto animal feed pellets. It may be unacceptable to allow any such larger droplets to be sprayed, if they would cause a few pellets to be grossly overdosed. There may be no opportunity for the large drops to be dispersed between many pellets if the pellets are absorbent, or if the large droplets strike the pellets near an outlet where there is less contact between pellets. Grossly overdosing a few pellets would either cause all the others to be underdosed, or would require larger quantities of liquid to be sprayed. For expensive liquids this wastage is undesirable. Trapping and recirculating the large droplets back into the sprayer head is impractical when spraying small quantities. In summary, it is important for accurate dosage that virtually all of the liquid injected into the sprayer is converted into small droplets and accurately directed onto the solids. The same problem of achieving accurate dosage requires the solids to be presented evenly to the spray. In a pan-type coater known from GB 1 499 591, items of food are tumbled while being sprayed. In another known device marketed by Amandus Kahl of D-21465 Reinbek, bei Hamburg, known as the ROTOSPRAY, pellets can be coated in an inverted conical shaped chamber. Liquid is sprayed horizontally from the centre of the chamber, and pellets are tumbled within the chamber. Distributor arms are rotated within the fixed chamber to bounce the pellets across the chamber into the horizontal spray. A further known liquid coater is marketed by Hough International. In this device an even circular curtain of pellets are dropped through a horizontal spray into a mixing chamber. In the mixing chamber, agitator arms blend and move the pellets towards a central discharge aperture. In all these known systems there are problems of uneven distribution of liquid, or wastage of liquid, or both. Uneven distribution of liquid may be caused by a short dwell time when pellets are exposed to the spray, or by unpredictable poorly controlled random tumbling of the pellets. Wastage of liquid may be caused by spraying an incomplete, random array of pellets therefore allowing the liquid onto the side walls or base of the coating pan, from where it may not be absorbed completely into the pellets. It is an object of the present invention to provide more accurate dosage of liquid sprayed onto solids. According to a first aspect of the invention there is provided a sprayer head for use in spraying liquids onto solids comprising; an inlet, means for dividing a flow of liquid from the inlet into droplets, a rotatable deflector mounted in the path of the droplets, and drive means for spinning the deflector. This enables large droplets to be broken up and redirected into the spray without wastage, and the spray output can be shaped as desired. Advantageously the deflector is substantially circular viewed along its axis of rotation. This assists in creating an even redistribution of droplets deflected by the deflector. Advantageously the path of the droplets has a main axis, and the deflector is mounted to deflect droplets away from the main axis, to create an annular curtain of spray. Advantageously the axis of rotation of the deflector is substantially parallel with the main axis. This helps to make the distribution of droplets within the curtain of spray more uniform. Advantageously the path of the droplets is substantially cone-shaped, and the deflector is mounted substantially centrally in the cone-shaped path so as to create a curtain of sprayed droplets around the deflector. Advantageously the means for dividing the flow comprises a rotatable blade. Advantageously the deflector and the blade are connected together and mounted . coaxially. This simplifies construction. Advantageously the means for dividing the flow comprises a housing for directing the droplets towards the outlet. Advantageously the deflector is sufficiently large and suitably positioned so as to intercept any line from the interior of the housing parallel to the main axis, to ensure droplets are not sprayed past the deflector along the main axis. According to a second aspect of the invention there is provided a pan-type coater for continuous spraying of liquid onto solids, comprising: means for feeding the solids onto the base of a pan to create a bed of solids on the base; a sprayer for spraying a zone of the bed of solids; a means for moving the solids on the base through the spraying zone towards an outlet; and a means for bringing solids from beneath the. surface of the bed, up to the surface of the bed, to expose substantially all of the solids to the spray for a substantially uniform dwell time. Advantageously the coater comprises a paddle means for moving the solids and/or bringing the solids to the surface. Advantageously the pan is rotatable relative to the means for moving the solids and/or bringing the solids to the surface. This gives simpler construction compared to making other parts of the coater rotatable. Advantageously the spraying zone comprises a ring around the centre of the pan. Advantageously the outlet is in the centre of the pan, and the inlet at the periphery, or vice versa. Advantageously the bed of solids is moved in a spiral path of at least 360° from the inlet to the outlet through the spraying zone. Advantageously the base is substantially horizontal. Advantageously the coater is arranged so that the average time any part of the bed remains in the spraying zone is 20 to 40 seconds. Advantageously the sprayer comprises a sprayer head as claimed in any of claims 1 to 10. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 shows a known sprayer head in schematic form; Figure 2 shows an embodiment of the present invention in schematic form; Figure 3 shows a plan view of the embodiment of Figure 2 in schematic form; and Figure 4 shows a side view cross-section of an embodiment of a pan-type coater of the present invention: Referring to Figure 1, a known sprayer head is shown, which produces a cone-shaped spray from the lower end of the centrifuge as represented in the Figure. According to a first embodiment of the invention, as shown in Figure 2, the known centrifuge is adapted by the addition of a rotatable deflector 4 in the form of a disc. As can be seen, this is mounted on a main axis 5 of the path of droplets created by the centrifuge. The rotatable deflector is caused to spin about the main axis due to the drive means constituted in this embodiment by the stem 6 which connects the deflector to the cross-beam 1 of the centrifuge. The centrifuge device for dividing a flow of liquid from an inlet into droplets is advantageous as it is not prone to clogging, and is adaptable for use with liquids having widely differing viscosities or other characteristics. The spray cone shape can be adapted by varying the air flow rate and the speed of rotation. For a more detailed description of this type of device, reference is made to EP-A-0 349 510, the contents of which is incorporated herein by reference. In operation, the rotatable deflector 4 catches any larger drips falling straight down from the centrifuge, and spins these drips outwards and disperses them into the main curtain of spray 7. Clearly the rotatable deflector could be driven independently from the centrifuge. When connected with the centrifuge, a speed range of 1000 to 10000 rpm is preferred. The speed should be sufficiently low that the spray does not become too fine and drift in suspension in the air, resulting in liquid losses. The speed should be sufficiently high that the spray is not uneven owing to the droplets being too large and a continuous curtain not being properly formed. The preferred speed depends to some extent on the diameter of the centrifuge and the rotatable deflector. With a diameter of 3 to 5 cm for the rotatable deflector, a rotation speed of approximately 4000 rpm is suitable. It is preferred if the diameter of the deflector matches the diameter of a housing 8 provided on the centrifuge for directing the droplets created. This ensures that the deflector intercepts any line from the interior of the housing parallel to the main axis to ensure droplets are not sprayed past the deflector along the main axis. The rotatable deflector may be smaller than the diameter of the housing, in which case the area to be sprayed can be increased, but with a risk of some sprayed droplets straying along the main axis. It will be apparent that the rotatable deflector is advantageously mounted so as to deflect droplets away from the main axis, but alternative configurations are conceivable in which the deflector is mounted off the main axis and deflects drops onto the main axis. The axis of rotation of the deflector is preferably substantially parallel with the main axis, but considerable deviation is conceivable. The sprayer head according to the present invention overcomes the problems of large droplets caused by the centrifuge or other types of apparatus for generating droplets. Any large droplets are returned into the curtain of spray without wastage. The invention also enables an annular cone-shaped curtain of spray to be created without causing more large droplets. The evenness of the distribution of the spray and the consistency of droplet size is also improved by the present invention, since the larger droplets are dispersed, and because the small amount of spray which would have been sprayed along the main axis, is redistributed . The pan-type coater as shown in Figure 4 will now be described. The coater comprises a sprayer 9 mounted above a pan 10. The sprayer may comprise a sprayer head as previously described with reference to Figures 1, 2 and 3. The pan is preferably a shallow cylindrical pan with a substantially horizontal base. The pan is mounted on a frame 11 using bearings 12 and a motor 13 is provided to drive the rotation of the pan through a transmission link 14 such as a belt. A pump 15 is provided for blowing air into the sprayer 9. Solids are fed onto the base of the pan by an inlet pipe 16 connected to a flow rate measurement device such as a continuous impact weighing device 17, or other weighing or volumetric measurement device. Paddles 18 are provided for moving the solids on the base of the pan. Because of the shape of the paddles, a moving bed of solids is created. The paddles may have two functions. Firstly, to move the solid towards the center of the pan, and secondly to turn the bed of solids to bring solids from beneath the surface up to the surface of the bed, where they are exposed to the spray. For the former function, a rectangular or triangular shape can be used, with a base of the triangle or rectangle lying against the base of the pan. Such a paddle can be mounted vertically and orientated so as to deflect the solids towards the center of the pan when the pan is rotated. The angle of the paddle relative to a radial of the pan can be varied according to the speed of rotation of the pan and the desired speed of flow of the bed of solids towards the center of the pan. One of these flat paddles can be positioned near the inlet to deflect solids towards the centre of the pan after going round once on the outside of the pan. For smoother deflection of the bed, the ends of the paddle can be bent towards the line of flow of the bed to give a gentle S-shaped plan view configuration. A single such paddle in the centre of the spraying zone can be sufficient. For the function of turning the bed of solids to expose lower parts of the bed to the spray, a paddle shaped like a plough can be used. For both functions, the height of the paddles can be arranged so as to ensure they are completely or almost completely covered by the bed of solids. Two plough shaped paddles may be arranged diametrically opposite one another in the pan. By varying the angle of orientation of the plough-shaped paddle, the two functions can be performed by a single paddle. Intermediate shapes of paddle combining the features of the various types of paddle described above can also be used. The paddles operate to move the bed of solids in a spiral motion towards the centre of the pan, through a spraying zone 19 on the base of the pan. The sprayer 9 is preferably arranged to spray in a well-defined circular hollow conical curtain 20. This creates a ring-shaped spraying zone around the centre of the pan. The coated solids are removed from an outlet, in this case formed by an aperture in the centre of the pan, through which the solids fall by gravity. For a more even coating, the speed of rotation of the pan and the arrangement of the paddle means is such that the solids are moved in a spiral of at least 360° while in the spraying zone. Again for improved evenness of coating, the average time any particular part of the bed remains in the spraying zone may be 5-60 seconds and should be preferably approximately 20-40 seconds, to ensure the solids are exposed regularly and evenly to the spray. A speed of 20-50 rpm is preferred, although a range of 5 to 100 rpm can be used. The pan-type coater as described achieves improvements in evenness of distribution and reduction of wastage of liquid. The combination of providing a bed of solids on the base of the pan, together with paddles for gently moving and turning the solids enables the bed to remain longer in the spraying zone. The gentle turning then enables substantially all the solids to be exposed on the surface for an average dwell time in the spraying zone which can be controlled according to the speed of rotation and the angle, position, and number of the paddles, to suit different types of solids. The feature of providing a continuous bed of solids ensures that there is no wastage of liquid. Also, the gentle moving and turning action which is implied in such operation, in contrast to the prior art, preserves the solids better from damage. Therefore less dust or fines is created. If the pan is rotatable and the paddles fixed, construction is simpler, and a centrifugal force acts on the bed of solids to push it away from the central outlet. This is beneficial in that the paddles need to exert a greater countering force to move the bed of solids towards the centre. A given change in flow rate towards the centre therefore requires a greater change in the orientation of the paddles. This reduces the range of change possible, but enables more accurate control of the rate of flow of the bed of solids. The centrifugal force also improves the action of the plough shaped paddles for similar reasons. Rotating the pan also has the advantage of evening out any lack of uniformity in the density of spray around the ring shaped spraying zone. A similar benefit would be possible by rotating the spraying means although this would involve more complex apparatus. A similar effect to the centrifugal force could be obtained by the force of gravity if the base of the pan were to be sloped upwardly towards its centre. In such a case the pan could remain stationery and the paddles and the inlet be rotated. Alternatively, the force of gravity could be used to assist the flow of the bed towards the central outlet by providing a base which slopes slightly downwards towards the central outlet. In each case, the slope could be up to 30° from the horizontal but should preferably be relatively gentle e.g. <5° so that there is little dependence on the coefficient of friction of the surface of the base. Also, any slope in the base should be relatively gentle so that the time the bed of solids is in the spray zone is not shortened unduly. Where the sprayer is mounted above the central outlet as shown in Figure 4, it is clearly advantageous if the spray is prevented from reaching the central portion of the pan. Here, where the solids fall through a central aperture, the distribution of solids becomes unpredictable, and impossible to control. Therefore evenness of distribution of the liquid onto the solids could be affected if the spray were allowed to reach this part, particularly is large droplets are allowed to drip from the sprayer head. Accordingly, it is advantageous if a sprayer head as described in relation to Figures 1, 2 and 3 is used with the pan coater of Figure 4. The amount of liquid sprayed can be closely controlled so as to conform precisely to the quantity of solids fed into the pan, by a controller (not shown) . The advantages of the present invention are particularly important when spraying very small amounts of liquid such as enzymes or other micro ingredients. When coating pellets of animal feed with very small amounts, e.g. in the region of 0.05 % by weight, of expensive enzymes, it is desirable to control the coating process very accurately to achieve a correct dosage for each animal. Such enzymes may have a response curve with a pronounced steep rise in response up to a given dose, then a flat response for larger doses. If the animal feeds are inaccurately coated with the enzyme, the optimium dose at the "break point" of the response curve is not achieved. If there is a wide variation in the amount of enzyme coated on each pellet (a large coefficient of variation) then a large proportion of the animals feed will either have too little enzyme, and therefore insufficient benefit, or too much enzyme and therefore the flat part of the response curve has been reached and the extra enzyme is wasted. The present invention enables the coefficient of variation to be reduced in spraying solids with liquids such as enzymes, so that the dose received by the animal can be more accurately controlled to be close to the optimum point on the response curve. Although the invention is suitable for spraying 1% wt or less, of liquid, it can be used for spraying larger proportions of liquid, up to 5% wt at least. Throughputs of 1-100 tonnes of solids per hour can be envisaged.

Claims: CLAIMS 1. A sprayer head for use in spraying liquids onto solids comprising: an inlet; means for dividing a flow of liquid from the inlet into droplets; a rotatable deflector mounted in the path of the droplets; and drive means for spinning the deflector. 2. A sprayer head as claimed in claim 1 wherein the deflector is substantially circular viewed along its axis of rotation. 3. A sprayer head as claimed in claim 1 or 2 wherein the path of the droplets has a main axis, and the deflector is mounted to deflect droplets away from the main axis. 4. A sprayer head as claimed in claim 3 wherein the axis of rotation of the deflector is substantially parallel with the main axis. 5. A sprayer head as claimed in any preceding claim wherein the path of the droplets is substantially cone-shaped, and the deflector is mounted substantially centrally in the cone-shaped path so as to create a curtain of sprayed droplets around the deflector. 6. A sprayer head as claimed in any preceding claim wherein the means for dividing the flow comprises a rotatable blade. 7. A sprayer head as claimed in claim 6 wherein the deflector and the blade are connected together and mounted coaxially. 8. A sprayer head as claimed in any preceding claim wherein the means for dividing the flow comprises a housing for directing the droplets. 9. A sprayer head as claimed in claim 8 when dependent on claim 3, wherein the deflector is sufficiently large and suitably positioned so as to intercept any line from the interior of the housing parallel to the main axis, to ensure droplets are not sprayed past the deflector along the main axis. 10. A sprayer head substantially as described with reference to the accompanying drawings. 11. A pan-type coater for continuous spraying of liquid onto solids, comprising: means for feeding the solids onto the base of a pan to create a bed of solids on the base; a sprayer for spraying a zone of the bed of solids; a means for moving the bed of solids on the base through the spraying zone towards an outlet; and a means for bringing solids from beneath the surface of the bed, up to the surface of the bed, to expose substantially all of the solids to the spray for a substantially uniform dwell time. 12. A coater as claimed in claim 11 comprising a paddle means for moving the solids and/or bringing the solids to the surface. 13. A coater as claimed in claim 11 or 12 wherein the pan is rotatable relative to the means for moving the solids and/or bringing the solids to the surface. 14. A coater as claimed in any of claims 11 to 13 wherein the spraying zone comprises a ring around the centre of the pan. 15. A coater as claimed in any of claims 11 to 14 wherein the outlet is in the centre of the pan, and the inlet at the periphery, or vice versa. 16. A coater as claimed in any of claims 11 to 15 wherein the bed of solids is moved in a spiral path of at least 360° from the inlet to the outlet through the spraying zone. 17. A coater as claimed in any of claims 11 to 16 wherein the base is substantially horizontal. 18. A coater as claimed in any of claims 11 to 17 arranged so that the average time any part of the bed remains in the spraying zone is 20 to 40 seconds. 19. A coater as claimed in any of claims 11 to 18 wherein the sprayer comprises a sprayer head as claimed in any of claims 1 to 10. 20. A coater substantially as described with reference to the accompanying drawings. 21. Use of a sprayer head as claimed in claims 1 to 10, or a coater as claimed in any of claims 11 to 20 for spraying solids with a liquid. 22. Use of a sprayer head as claimed in claims 1 to 10 or a coater as claimed in any of claims 11 to 20 for spraying solids with < 1% wt of liquid.

Inventors: NISSINEN VESA JUHANI, SCHRAUWEN DIRK RENE GERMAINE, SCHRAUWEN LUC JOHN MARIA, NISSINEN, VESA, JUHANI, SCHRAUWEN, DIRK, RENE, GERMAINE, SCHRAUWEN, LUC, JOHN, MARIA
Applicants: FINNFEEDS INT LTD, NISSINEN VESA JUHANI, SCHRAUWEN DIRK RENE GERMAINE, SCHRAUWEN LUC JOHN MARIA, FINNFEEDS INTERNATIONAL LTD., NISSINEN, VESA, JUHANI, SCHRAUWEN, DIRK, RENE, GERMAINE, SCHRAUWEN, LUC, JOHN, MARIA
Application year: 1994
Main classification: B05B3
IPC codes: A23G3, B01F5, B05B3